Process for the production of an artificial leather and the resultant product

ABSTRACT

PRODUCTION OF AN IMITATION OR ARTIFICIAL LEATHER BY IMPREGNATION OF A NON-WOVEN FIBROUS WEB IN SUCCESSIVE OR SEPARATE STEPS WITH A SOLVENT SOLUTION OF AN ELASTOMER SUCH THAT INCREASING CONCENTRATIONS OF THE ELASTOMER ARE SUPPLIED OVER THE THICKNESS OF THE WEB, IMMEDIATELY COAGULATING THE WEB IN A CONVENTIONAL BATH AFTER THE LAST SOLUTION OF THE ELASTOMER HAS BEEN APPLIED AND THEN WASHING AND DRYING THE WEB TO PROVIDE A FIBER-REINFORCED MICROPOROUS ELASTOMERIC STRUCTURE CLOSELY RESEMBLING NATURAL LEATHER.

June 27, 1972 G. SEIBERT 3,672,943

PROCESS FOR THE PRODUCTION OF AN ARTIFICIAL LEATHER AND THE RESULTANTPRODUCT Filed July 14, 1970 4 AQUEOUS PRECIPITATING BATH/ FIG, 2

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GERHARD SEIBERT KLAUS GERLACH BYQ W W M W Y ATTYS United States Patent3,672,943 PROCESS FOR THE PRODUCTION OF AN ARTI- FICIAL LEATHER AND THERESULTANT PRODUCT Gerhard Seibert, Erlenbach, and Klaus Gerlach,Obernau, Germany, assignors to Glanzstoif AG, Wuppertal, Germany FiledJuly 14, 1970, Ser. No. 54,787

Claims priority, application Germany, July 16, 1969,

Int. Cl. D06m 3/00; B44d 1/16 17 Claims US. Cl. 117-63 ABSTRACT OF THEDISCLOSURE As is well known, an imitation leather can be produced fromfibrous mats, webs or fleeces which are impregnated with an elastomericbinder to form a flexible, porous sheet which may then be coated with atop layer. The base material or substrate used for this purpose ispreferably a fibrous fleece or non-woven web which has been produced bycarding or by manufacture on a paper machine and which has beenstrengthened by mechanical means, for exampleby stitching or by someother treatment such as heating. Impregnation is carried out using asolution or gel of a synthetic elastomeric polymer, polyurethanes beingparticularly suitable, with which the web is treated so that thesolution or gel completely penetrates the fibrous substrate. Aftercoagulation of the elastomeric polymer in a conventional precipitationbath, the solvent is washed out and the product dried, a substrate orbase layer thus being produced in which approximately 20 to 75 parts byweight of the elastomeric binder are uniformly distributed in 80 to 25parts by weight of fibers. To. produce imitation leather with a smoothsurface, fibrous webs which have been treated with the binder andhardened into the porous substrate are then ground on at least onesurface and then provided with a top layer, e.g. a thin surface layer ofthe same elastomer or another suitable polymer.

Although imitation leathers which can be manufactured by known processeshave certain very advantageous properties, such as fine pores,flexibility, abrasion resistance and the like, they still differconsiderably from natural leather in their structure. As is well known,natural leather comprises a very compact upper surface (grain side) anda less dense, more fibrous underside (flesh side), a structure which hasnot previously been achieved in an imitation leather. The top layer orsurface coating of an imitation leather cannot simply be compared withthe grain side of natural leather because some of the most importantproperties such as stretching or elongation, density and compressibilityare very different from those of natural leather. Other particularlyvaluable properties of natural leather, such as bending characteristics,the soft handle of its underside and the absence of the so-called orangepeel effect are due to the distinctive structure of natural leather.Many attempts have been made to produce an imitation leather'whichresembles natural leather as closely as possible. However, previousattempts to obtain a top 3,672,943 Patented June 27, 1972 surfacesimilar to the grain side of natural leather have not been satisfactory,even when combining the impregnated fibrous substrate with a coatedfabric.

It is a primary object of the invention to produce an imitation leatherwhich more closely resembles natural leather in its entire structure.

Another object of the invention is to provide a process for theproduction of an imitation leather employing conventional non-woven websand elastomeric binders to achieve a microporous, flexible,fiber-reinforced elastomer layer having a variation in itscross-sectional properties quite similar to natural leather. Otherobjects and advantages of the invention will become more apparenthereinafter.

According to the present invention, it has now been found that asubstantial improvement can be achieved in a process for the productionof an imitation leather by the steps comprising successively applying aplurality of said solutions of elastomer onto one surface of a movingnonwoven fibrous web at intervals along said surface spaced sufficientlyto permit a substantially complete penetration of one solution into theWeb before application of the next succeeding solution, the individualsolutions having an increased concentration of the elastomer in eachsucceeding application, conducting the impregnated web through aprecipitation bath to coagulate the elastomer after the last solution ofthe elastomer has been applied, washing solvent from the web containingthe coagulated elastomer, and drying the washed web.

Alternatively, it is also possible to apply a first solutionof elastomerto the lower surface of the moving nonwoven fibrous Web while thenapplying only one additional solution having a substantially greaterconcentration of elastomer to the upper surface of the moving web at apoint of time which is not substantially prior .to the application ofthe first solution to the lower surface, i.e. so that impregnation ofthe upper surface occurs at-approximately the same time or shortly afterimpregnation of the lower surface. The applications of the elastomersoltuions of different concentrations from below and above the fibrousweb must be regulated in place and amount such that a partialoverlapping of impregnated layers of separate solutions is provided fromtop to bottom over the thickness of the web. With these partiallyoverlapping impregnations, the web is then coagulated, washed and driedto provide a microporous layer of increasing density from the bottom tothe top thereof.

The process of the invention is especially advantageously carried out bycombining both of these techniques in the following manner. A solutionof an elastomer polymer is applied to the underside or lower surface ofthe fibrous web, preferably by means of a roller applicator, and at thesame time or thereafter a plurality of at least two elastomer solutionsare successively applied to the upper surface of the moving web. Thesolution applied to the lower surface of the mat has a lowerconcentration of the elastomer than any of the solutions applied to theupper surface of the mat and, with several solutions being applied tothe upper surface, the elastomer concentration of that solution which isapplied at a later stage is higher than that of the solutions previouslyapplied. The distances or intervals between the different positionswhere the solutions are applied to the upper surface of the web are sochosen that before a new solution is applied, the one previously appliedhas already penetrated into the surface of the web.

Thus, it is desirable to regulate the application of all of theelastomeric solutions as to point of application and amount so as toprovide a partial overlapping of each adjacent layer of impregnatedseparate solutions from the top to the bottom of the thickness of theweb.

The initial material used for the fibrous fleece or web to beimpregnated advantageously consists at least partly of synthetic fibresand exhibits a density of 0.08 to 0.30 g./cm. and preferably 0.12 to0.20 g./cm. These webs or fleeces may be produced in a conventionalmanner by carding or by a process of deposition from water on apaper-making machine, and then consolidated or strengthened in knownmanner by stitching and/or by a heat treatment.

The concentration of the elastomer solutions should preferably extendover a range from about 8 to 35% by weight, preferably between 12 and30% by weight. The concentrations of the individual solutions, which areapplied separately to the non-woven web, are preferably adjusted to thedensity of the inital web so that the finished product will have aslarge as possible a difference in density between the upper surface andthe lower or bottom surface.

Although it is feasible to employ an initial web of somewhat increasingdensity from bottom to top in order to enhance the desired effect, it isan advantage of the invention that the initial web itself may be ofsubstantially uniform density. As a general rule, it has been found thatin using a fibrous web of comparatively low uniform density, adifference in concentration between the different elastomer solutionshas a more pronounced effect in producing a variations in the densityover the thickness or width of the finished product than in webs ofhigher uniform density. On the other hand, comparatively more highlyconcentrated solutions should be used for initial fibrous webs of lowerdensity.

In order to produce imitation leather which has a very high density onits upper surface and thus resembles natural leather very closely in itsstructure, additional compacting or compression of the fibrous web isadvantageously carried out, preferably during coagulation of theelastomer in the precipitation bath. This may be achieved by compressingthe completely impregnated fibrous web between rotating rollers in anaqueous precipitating bath after coagulation of the impregnatedelasmeric binder has started. This may be carried out in several stages,for example by passing the impregnated Web successively between severalpairs of nip or pinch rollers with decreasing distances between the tworollers of each pair. In this way, for example, the density at the uppersurface of the finished imitation leather can be increased by to 60%, ascompared to that of the product which has not been compressed.

impregnating materials which are especially suitable for this processare solutions of polyurethanes is dimethylformamide or in similarorganic solvents known for this purpose. The handle and suppleness ofthe imitation leather can be improved by adding 5 to 30% by weight ofparaffin oil or silicone oil (based on the weight of elastomer) to theelastomer solution applied to the bottom surface of the web. Theelastomer solution or solutions applied to the upper surface may containup to by weight, based on the total polymer content of a vinyl chloridepolymer such as polyvinyl chloride or vinyl chloride copolymers. Thisimproves the capacity of the material to be fixed by heat, which isespecially important if the imitation leather is to undergo subsequentprocessing commonly employed in the shoe industry.

In general, the process of the invention is applicable to anysolvent-soluble synthetic elastomeric binder capable of being coagulatedinto a vapor-permeable and preferably microporous film or substrate.These elastomeric polymer binders are referred to more simply aselastomers. Suitable elastomers and their solvents as well asnon-solvents employed to gel or coagulate the dissolved polymer aredisclosed in great detail in the prior art, for example as set forth inU.S. Pats. No.

2,871,218, No. 3,190,766 and No. 3,208,875. The polyurethanes exhibitespecially desirable leather-like qualities whether used along or incombination with other wellknown elastomeric polymers or even smallamounts of non-leastornen'c polymers. For this reason, the use of apolyurethane elastomer is especially preferred without excluding minorproportions of other'suitable elastomers. Moreover, it is desirable toselect an elastomer which can be dissolved over the broadest possiblerange of concentration consistent with subsequent coagulation andformation of a vapor-permeable structure, and the polyurethaneelastomers are especially suitable for this purpose. Of course, otherknown additives may also be included in the initially prepared elastomersolutions, usually in very minor amounts although the solution formingthe top layer in the process of the invention may contain relativelylarger amounts of other elastomers and/or compatible additives.

The process according to the invention is relatively simple and can becarried out continuously with conventional and rather inexpensiveapparatus. The process is further illustrated by means of theaccompanying drawings in which:

FIG. 1 is a schematic flow sheet or side elevational view of suitableapparatus for continuously carrying out the process of the invention;and

FIG. 2 is a diagrammatic longitudinal cross-sectional view on anenlarged scale of the non-woven fibrous web undergoing impregnation withdifferent elastomer solutions.

In FIG. 1, a substantially dry non-woven fibrous web is continuouslysupplied by means of a pair of feed rollers 2 and passed over a rollerapplicator 3 which rotates in a vat 4 containing a first polyurethanesolution of relatively low concentration. A stripping knife 5 isdirected toward the surface of the roller just before its point ofcontact with the fibrous web. The distance of this knife 5 from thesurface of the roller may be, for example, about or A the thickness ofthe fibrous web, the thickness of layer of polyurethane remaining on thesurface of the roller and transferred to the fibrous web beingsubstantially equal to a predetermined set interval between the knifeand the surface of the roller. The polyurethane solution penetrates thefibrous web from the bottom side and is absorbed relatively quickly bythe web. 7

A doctor knife 6 is arranged above the roller 3 to sup ply an elastomersolution onto the top surface of the web, this second solution having asubstantially higher concentration of elastomer than the first solutionA. In order to obtain an initially formed layer of elastomer solution Bhaving the required thickness, the width of the gap between the doctorknife 6 and the surface of the web 1 is adjusted to about A or of thethickness of the fibrous web. Since the rate at which the elastomersolution penetrates the web depends partly on the viscosity of thesolution, i.e. the quantity of binder used for impregnation is notdetermined entirely by the width of the gap between the doctor knife andthe surface of the web, it is advisable to determine the most suitablewidth of the gap by a few trial adjustments. After the point or shorttransverse zone of application of the solution'B, the fibrous web iscarried along freely until the applied coating or layer applied haspenetrated into the fleece. This point of penetration is easilyrecognized since the surface of the web then appears to be fibrous andalmost dry.

Another elastomer solution C of still higher concentration than eitherof the solutions A and B is then applied 1 onto the top surface of theweb 1 by means of a doctor knife 7, in this case arranged above a roller8. Here again the width of the gap between the doctor knife 7 and thesurface of the web 1 is adjusted'according to the thickness of the layerof elastomeric impregnating agent which is to be applied to the fibrousweb, as explained above. As soon as this layer C has penetrated into theweb, thecontinuously moving web passes between a pair of nip rollers 9which exert a very slight pressure on the fleece in order to relativelyeven out the impregnation but without squeezing off any elastomersolution or changing the relative positions of the separately appliedlayers.

Thereafter, a fourth elastomer solution D of highest concentration isapplied by means of a doctor knife 11 arranged over a roller 10. Lastly,the web, which is now completely impregnated with elastomer solutions isintroduced into a vat 12 containing water as a non-solvent precipitatingbath in which coagulation of the elastomeric binder takes place.Subsequent treatment can-also be carried out continuously in knownmanner inconventional apparatus (not shown) arranged after the vat, thesolvent first being washed out and the resulting porous product thendried. The impregnated fibrous web after being dried can be wound andstored. Also, it may then be ground to smooth the top surface andprovided with a top layer of an elastomer such as the preferredpolyurethane. Alternatively, the material may be directly subjectedtothe usualleather finishing treatments immediately after drying,especially if the last applied layer of polyurethane has not beenpermitted to completely penetrate into the top surface beforecoagulation. I I

The process explained with reference to FIG. 1 may, of course, bemodified within the scope of the invention. For example, fewer or morethan threeelastomer solutions may be applied successively to the topsurface fibrous web, provided the concentration of the solutionsincreases with each successive application.

In general, however, it is usually desirable to employ a minimum ofthree separate elastomer solutions, one of which can be impregnated fromthe bottom surface, up to a maximum of about five or six separateelastomer solutions depending upon the total thickness of the initialnonwoven fibrous web and excluding any final top surface coating whichdoes not fully impregnate the web.

v The process illustrated in FIG. 1 may also be modified in that all thesolutions may be applied to the upper surface of the web or, instead ofapplying solution B in approximately the same location as solution A, itmay be applied at some distance displaced from the location ofapplication of solution A in the direction of continuous movement of thefibrous web. In this case, another combined assembly of doctorknife andguide roller is arranged after the guide roller.3.

Furthermore, it is not absolutely necessary to provide a pair of rollers9 between the points of application of solutions '0 and D. On the otherhand, such pairs of nip rollers, which even out the application of theimpregnation as described more fully below, may be arrangedadvantageously between every two points or zones of application of thedifferent solutions. Also, afterentering the aqueous bath 12, where theweb is transported on suitable guide rollers 12a (usually over a greaterlength thanthat shown in the drawing), one or more pairs of compressionrollers 12b can be employed during coagulation to further increase theelastomer density.

. As a general rule, the individual elastomer solutions are mostconveniently applied by means of a knife or doctor blade except forthose instances in which the first solution A is applied to the bottomsurface where a roller applicator is preferred. In all cases, it ishelpful to apply approximately equal thicknesses of the solution layerswhich are intended to fully impregnate the fibrous web and in such anamount that the last of such layers of elastomer solution willsubstantially completely impregnate into the web so that the void spacesbetween fibers is filled or almost filled. Thus, with three separateelastomeric solutions, disregarding a final top layer which remains atleast partially above the web surface, the individual impregnated layerscan each be about onethird of the thickness of the initial dry web. Thisprocedure is of course subject to a relatively broad variation, but itwill generally be found preferable to employ variations in such a mannerthat those solutions with the lowest concentration of elastomer areapplied in wider or thicker layers while the more concentrated solutionsare correspondingly reduced in thickness.

The primary object of a carefully regulated application of individualelastomer solutions of different concentra tion is to achieve animpregnated web with a moreor less gradually increasing content of theelastomer from the bottom surface to the top surface. The nip rollers 9located between the last fully impregnated solution C and the topcoating D and/or between preceding impregnated solutions B and C havethe effect of achieving not only a more uniform evening out ofindividual layers of solution but also a bringing together of theapplied layers internally of the web and ensuring a partial overlappingof the layers in terms of a variation in the concentration content ofelastomer over the thickness of the web. The liquid solvent in eachlayer is somewhat more fluid or exchangeable between adjacent layers,and by using a very slight pressure on the completely or partiallyimpregnated web, there occurs a blending of the fluid solutions at theirinterfaces and a corresponding transfer of one layer of moreconcentrated elastomer into the next adjacent layer of less concentratedelastomer. It will be understood, of course, that such evening out orblending of the solution layers must not cause any substantial removalof solvent, and a complete blending of one layer with another must beavoided. Therefore, depending upon the viscosity of the layers, it isoften preferred to avoid using the nip rollers 9 or else employ themonly under an extremely slight pressure since there is a naturaltendency for the layers to blend by themselves.

In this respect, it is also generally preferred to apply successivelayers of the elastomer solutions as closely together as possible, e.g.by adding a succeeding layer almost immediately upon disappearance ofthe preceding layer'into the surface of the web. Also, once the web isfully impregnated, with or without a top covering or coating layer, itis generally desirable to conduct the impregnated web immediately intothe coagulating bath, i.e. without undue delay so as to preventexcessive blending one solution layer into the next adjacent layer. Theallowable time of delay will of course also depend upon the relativeviscosity of the individual elastomer solutions and the extent to whichblending has been promoted by slightly compressing the web prior to itsentry into 7 the precipitating bath. Once the impregnated elastomericbinder begins to coagulate, it is believed that this blending betweenadjacent layers is stopped or at least substantially retarded since theviscosity of the layers increases rapidly with gelling or coagulation.

Once the impregnated web is being coagulated or hardened in theprecipitating bath, a considerably greater pressure can be appliedthereto by one or a plurality of nip rollers. Surprisingly, this leadsto a much greater increase in the density of the uppermost layer and apro portionately smaller increase in density of the next lower layers,the smallest increase in density appearing in the bottom layer oforiginally the least concentration. This effect not only enhances thedesired variation in density but also tends to provide a more compactand stronger product with excellent surface characteristics as betweenthe so-called grain side and flesh side of the imitation leather.

The overlapping or blending processes which occur when impregnation iscarried out in several stages are illustrated diagrammatically in FIG.2. The initially dry fibrous web 13 is shown on a scale which is greatlyenlarged compared to the linear indication of the web 1 shown in FIG. 1.This web 13 corresponds to a longitudinal cross-section of a shortlength of the moving web, the arrow indicating the continuous directionof open space bounded by the top surface 13a and the bottom surface 13b.

, The elastomer solution A is applied to the bottom side. 1311 of theweb by means of the roller 14. This first layer A of the impregnatingagent on roller 14 is stripped oif by means of a knife (not shown) to athickness equal to about /3 of the thickness of the fibrous web 13.Owing to therelatively low viscosity of solution A, it penetrates fairlyrapidly into the fleece which is being moved forward, andit becomesdistributed over the shaded area or thickness of the web roughlyindicated by the reference numeral 15. The solution B, which is morehighly concentrated, is applied at a position transverse to the movingweb and approximately directlyabove the axis of the roller 14'by meansof a doctor blade 18. Owing to its higher viscosity, thissolution Bpenetrates the fleece slightly 'more slowly and becomes distributed asthe shaded layer 16 in the fibrous web. SolutionC, the distribution ofwhich is indicated by the referencenumeral l 7 ,'"i s applied withdoctor blade 19 to the top surface 13a of the web at the transverselocation 17 when no.

more-ofthe impregnating agent or solution B can beseenonthe surface ofthe web, i.e. when the surface appears almostdry. Owing to the stillhigher viscosity of this solution C and the solutions already present inthe web solution C, penetrates evenmore slowly. Theboundaries of thelayers of impregnating agent. 15, 16 and 17 are not sharpQbut-blurred orblended together. Viewed as a whole, it is precisely due to thesegradual transitions from one layer of an elastomer solution to the nextin the fibrous web that the density of the elastomer material increasesmore or less continuously from the bottom surface 13b to the uppersurface 13a in the finished imitation or synthetic leather product.

The accumulation of elastomer solution on the lower edge of the doctorblades 18and 19 has also been greatly exaggerated in FIG. 2, since it isgenerally desirable to maintain the level of such accumulating binder orimpregnating agent at about the height of the short gap between theblade 18 or 19 and the top surface 134; of the web. This can beaccomplished very easily by regulating the flow of elastomer solutiondown the inclined edge of each doctor blade as indicated in FIG. 1 or byemploying a suitable metering feed trough or other conventional feedmeans for continuouslysupplying elastomer solution directly to the tipof the doctor blade at a predetermined rate.

The application of the top coating or layer of elastomer D as shown inFIG. 1 is optional, for example to ensure a final complete impregnationof the web or an excess surface coated layer to completely hide thefibrous material of the web, e.g. to prevent any loose ends or loopsfrom projecting from the top surface. When used. for this latterpurpose, a special elastomer composition may be.

employed to provide a relatively thin but dense and abrasion-resistantsurface coating. On the other hand, the

elastomer concentration of D may be approximately the same as thatofsolution C, simply to provide a finish-' ing touch or final filling ofthe web to provide avery uniform top layer just before coagulation.These and other variations can obviously be carried out, e.g. such asgrinding and/or bufling the surfaces of the finishedtions and thestepwise application of these solutions successive operations accordingto the invention ensure the formation of a structure which resemblesthat of natural leather to a much greater extent than'has been achievedprior to this invention. With a very' thin non woven fibrous web, it isfeasible to employ only one top layer and onebottom layer of elastomersolution applied onto the'opposite side or surfaces of the web. Even.though the variation in density is somewhat less in this case, it can beimproved by preferably preblending the layers with slight compressionbefore entering the pre- 8 cipitation bath and further compressing theweb during coagulation in the bath.

The final products produced in accordance with. the.in-. vention exhibita finely porous, dense grain side 7 (upper surface) and a softer,fibrous flesh side (bottom,surface). This structure can be clearlyobserved when the synthetic leather is split. The split layers, moreoverdistinctly exhibit a firmness which'decreases and a pore size whichincreases from the upper surface to the bottomsurface of the syntheticleather.

The process of the invention is further illustrated in detail byreference to the following examples, it being understood that theinvention .is not restricted to such examples.

EXAMPLE 1 A non-woven fleece or web is prepared from an aqueousdispersion of nylon fibers and regeneratedcellulose fibers (in a weightratio of polyamidezviscose fibers of :20) by 'deposition'onapaper-making machine, and the waterlaid web is consolidated, i-.e.,rendered more strongly coherent, by a brief heat treatment. The dryfibrous web has a weight of 310 g./m a density of 0.13 'gl/cmfiand athickness of 2.4 mm. e

'Thefollowing elastomer pregnating'the web: Solution A:

solutions are used for im- Percent by Polyurethane 14.0Dimethylformamide 78.0 SiIicone oil 2.0 Water 6,0- Solution B: I j jPolyurethane 16.5 :Dimethylformamide 77.5 Water i 6.0 Solution C: p j pi f Polyurethane 20.0

V Copolymer of vinyl chloride and maleic acid anhydride .1; 7.0Dimethylformamide j i Water j"3.0

The polyurethane used inall solutions is the reaction product ofpolybutylene adipate'having an average 'molecular weight ofapproximately 1000, diphenylmethanetfl' diisocyanate and butanediolin amolar ratio *or1;'3.1 :211.

The silicone oil is a phenylmethyl"polysiloxane with a with solution A.A knife is arranged just beforethepoint ofcontact 'between'the rollerand the bottomsuiface or; the web-at a short distance from the rollersurface in order to strip the solution-A to a layer thickness of'0.'5

mm. The elastomersolution transferred to the bottonr surface of thewebisthereby applied in a thickness correspondingtoabout 0.5 kilogramper square meter: of the web. Solution B-is applied at the'same time bymeans of a doctor blade situated above the webin line wim'meaxis of theroller-situated below-the web. The gap be tween the doctor blade: andthe upper surface of'the' web is 0.6 mm. Solution B is thereby appliedat the rate of 0.77 kg.-/m-.3-of.the web. e s

After the roller applicator and the first doctor-blade, the web orfieeceruns freely for alength 0150.6 meter (60 cm.) and is then passedbetween a pair of hip rollers providing a slight pressure. Before theweb enters this pair of ;niprollers, the solution-B has completely'pene- I trated into the fibrous web, i.e.'so .that the surface of the Idistance of 0.5'meter (50 cm.) beyond the pair of'nip rollers, the webis conveyed over a guide roller arranged to cooperate with a seconddoctor blade, which is arranged at a gap distance of 0.7 mm. from thetop surface of the web and applies solution C at the rate of 0.8 kg. ofsolution per square meter of fibrous web.

At a distance of 2 meters (200 cm.) beyond the guide roller and seconddoctor blade, the web enters a bath of water maintained at a temperatureof 40 C. in which the elastomers are coagulated and the solvent iswashed out to form a porous elastomeric structure. The web is then driedcarefully under conventional conditions to maintain the desired porousstructure. The finished synthetic leather weighs 715 g./m.

To determine its density, the finished product is split into threelayers of equal thickness, each layer amounting to 0.64 mm. Thedensities of these layers taken in order from the bottom surface to theupper surface, are found to be 0.29, 0.34 and 0.48 g./cm. respectively.

In a second experiment under otherwise the same conditions but whereinabout 80 seconds after immersion in the precipitation bath, by whichtime coagulation of the impregnated elastomer has already begun, thecompletely impregnated fibrous web is passed successively between 6pairs of nip rollers which are arranged about 40 cm. apart in the bath,each pair of rollers exerting a force of 9 kg./ cm. on the web. Animitation or synthetic leather which has a'wei'ght of 705 g./m. is thenobtained after drying. The three layers, each 0.41 mm. in thickness,obtained by splitting as in the preceding experiment are found to havedensities of 0.45, 0.52 and 0.73 g./cm. respectively.

EXAMPLE 2 The process described in Example 1 is repeated, using a dryfibrous web of the aforesaid composition which has a thickness of 2.53mm. and a density of 0.13 g./cm. The polymer solutions used insuccession have the following compositions:

Solution A:

Polyurethane Percent by wt. 16.0

- The polyurethane used in this instance was prepared by reactingpolybutylene adipate (molecular weight of approximately 1000),diphenyhnethane-4,4'-diisocyanate and butanediol in proportions of 1:2:1.

After application of the solutions in the same manner as described inExample 1, the impregnated web is passed through the water bath withoutany appreciable application of pressure during coagulation. Theresulting imitation leather after being dried has a weight of 775 g./m.and a thickness of 1.29 mm. The densities of the three split layers,each 0.43 mm. in thickness, are 0.52, 0.60 and 0.68 g. cm. respectively,measured in the order of the layers from bottom to top.

EXAMPLE 3 Solution A: Percent by wt. I Polyurethane 14.0 Paraflin oil2.0

10 Solution A: Percent by wt. Water 6.0 Dimethylformamide 78.0 SolutionB:

Polyurethane 16.5 Water 6.0 Dimethylformamide 77.5 Solution C:

Polyurethane 20.0 Vinyl chloride copolymer of Example 1 5.0 Water 4.0Dimethylformamide 71.0

The polyurethane in this instance was prepared by reacting polybutyleneadipate (molecular weight of approximately 1000),diphenylmethane-4,4-diisocyanate and butanediol in the ratio of 1:2.5:1.5.

The coagulation treatment in the aqueous bath is carried out withoutapplication of pressure. The resulting imitation leather has a.weight of778 g./m. and a thickness of 1.75 mm. The three split layers, each of0.58 mm. in thickness, have densities of 0.33, 0.46 and 0.56 g./cm.respectively.

EXAMPLE 4 A fibrous web having a density of 0.145 g./cm. and a thicknessof 2.81 mm. is again impregnated as in Example 1 with three distinctsolutions of the following compositions:

The polyurethane was prepared by reacting polybutylene adipate(molecular weight of approximately 1000),diphenylmethane-4,4-diisocyanate and butanediol in the ratio of1:2.25:1.25.

After treating the impregnated fibrous web for coagulation of theelastomers without application of pressure followed by washing anddrying, the finished imitation leather product had a weght of 885 g./m.and a thickness of 2.40 mm. The three split layers, each of 0.80 mm. inthickness, have densities of 0.29, 0.36 and 0.45 g./cm. respectively.

When coagulation is carried out under pressure as in the secondexperiment of Example 1, an imitation leather product having a weight of874 g./m. and a thickness of 1.62 mm. is obtained. The split layers of0.54 mm. in thickness have densities of 0.41, 0.50 and 0.63 g./cm.respectively.

EXAMPLE 5 A fibrous web of 1.85 mm. in thickness and having a density of0.22 g./cm. is used as the initial material and is impregnatedsuccessively as in Example 1 with solutions having the same compositionas indicated in Example 4.

The imitation leather, which is slightly compacted during coagulation,exhibits a weight of 687 g./m. and a thickness of 1.31 mm. The splitlayers, which are 0.41 mm. in thickness, have a density of 0.47, 0.52and 0.67 g./cm. respectively.

EXAMPLE 6 Starting with the same non-woven fibrous web as in Example 5,impregnation is carried out in three stages 1 1 under the sameconditions as indicated in Example 1. The solutions applied insuccession have the composition set forth in Example 2. Coagulation ofthe polymer is then carried out without application of pressure andconventionally washed and dried. The imitation leather product has aweight of 705 g./m. and a thickness of 1.31 mm. The split layers have athickness of 0.4 mm. each and densities of 0.48, 0.52 and 0.62 g./cm.respectively.

Similar results are achieved when all three of the clastomer solutionsare applied and impregnated into the top surface of the fibrous web.However, the results are somewhat more uniform when applying thesolution of lowest concentration by means of a roller applicator to thebottom surface of the web. Likewise, it is possible to achieve verysatisfactory results, when using three, four or even more successivelyadded solutions of increasing elastomer concentration in addition to thesolution impregnated into the bottom surface. Moreover, when thefinished synthetic leather product is split into increasingly smallerlayers, for example by halving the first three split layers, a verydesirable gradual increase in density from bottom to top can be morecompletely identified.

It is not essential to further treat the initially coagulated, washedand dried product of the invention since it can be immediately used as anon-finished leather-like product, although it is usually desirable inthis case to apply the top layer or a final surface coated layer justprior to coagulation. In order to fully develop the grain side of theproduct of the invention, it can be buffed or polished and then furthercoated with a thin film-forming polymer or still another microporouselastomeric layer as is often required for synthetic shoe leathers,especially so as to provide -a water-impervious but vapor-permeableouter surface. Otherwise, the smoothed or developed grain side of theproduct according to the invention can be merely dyed or finished in thesame manner as normally observed for the conventional treatment of bothnatural and synthetic leathers.

Both the visual appearance and the physical properties of the syntheticleather materials of the present invention are so closely related tonatural leather as to provide an excellent substitute for a very widevariety of leather applications.

The invention is hereby claimed as follows:

. 1.In a process for the production of an imitation leather" wherein anon-woven fibrous web is impregnated with a solvent solution of anelastomer capable of being coagulated and hardened into a microporouselastomeric structure, the impregnated elastomer is coagulated byimmersion in a precipitation bath, solvent is washed from the webcontaining the impregnated and coagulated elastomer and the resultingwashed web is dried, the improvement which comprises:

successively applying a plurality of said impregnating solutions ofelastomer onto one surface of a moving non-woven fibrous web atintervals along said surface spaced sufliciently to permit asubstantially complete penetration of one solution into the web beforeapplication of the next succeeding solution, theindividual solutionshaving an increased concentration of the elastomer in each succeedingapplication and the total amount of said individual solutions beingsulficient to provide at least two partially overlapping impregnationswithin said web; and conducting. the impregnated web through aprecipitation bath to coagulate the elastomer only after the lastsolution ofthe elastomer has been applied. 2'. A process as claimed inclaim 1 wherein one solvent solution of the elastomer is applied to thelower surface of the moving web from a roller applicator whilesuccessively applying said plurality of other solvent solutions ofelastomer to the upper surface of the moving web such that the first ofthe applications to the upper surface occurs at a point of time which isnot substantially prior to the application of said one solution to saidlower surface, the

12 solution applied to said lower surface having a lower con: centrationof elastomer than anyv of thesolutions applied to the upper surface. v

3. A process as claimed in claim 2 wherein the solvent solution appliedto the lower surface of the web contains. about 5 to 30% by weight, withreference. to the weight of elastomer, of parafiin oil or silicone oil.

4. A process as claimed in claim 1 wherein the increasing concentrationof the elastomer in succeeding applications from a solvent solutionranges between about 8 and 35% by weight.

5. A process as claimed in claim 1 wherein the increasing concentrationof the elastomer in succeeding applica-: tions from a solvent solutionranges between about 12 a nd 30% by weight. 1 a w 6. A process asclaimed in claim 1 wherein the initial non-woven fibrous web to beimpregnated has a density of from about 0.08 to 0.30 gram/cm. v

7. A process as claimed in claim 1 wherein said elastomer consistsessentially of polyurethane.

8. A process as claimed in claim 7 wherein the last applied solutioncontains up to about 35 by weight,- with reference to the polyurethaneelastomer, :of aavinyl chloride polymer.

9. A process. as claimed in claim 1 whereinthe im-' pregnated web iscompressed in the precipitation bath: during coagulation of theelastomer. I 1

10. A process as claimed in claim 1 wherein there are at least threesucceeding applications of said solvent solu-# tion of elastomer.

11. The imitation leather product obtained by the process of claim 1exhibiting a graduallyincreasing density over the thickness of theimpregnated non-woven-fibrous web. I

if 12. In a process for the production of an imitation leather wherein anon-woven fibrous web is-impregna'ted with a solvent solution of anelastomer capable of being coagulated and hardened into a microporouselastomeric structure, the impregnated elastomer is coagulated byimmersion in a precipitation bath, solvent is washed from the webcontaining the impregnated and coagulated elastomer and theresultingwashed'web is dried,,the' improvement which comprises: 7

applying a first solution of elastomer to the lower surface of themoving non-woven Web; I I E applying at least one additional solution ofthe elastomer to the upper surface of the moving web at a point of timewhich is not substantially prior to the application of the firstsolution to'said lower surface, the concentration of elastomer in saidat least one additional solution applied to' the upper surface beingsubstantially greater than the concentration of elastomer in said firstsolution and said concentration of elastomer being increased in anysuccessive applica-. tions of more than oneto said upper surface, all ofthe' applications of elastomer solutions being regulated as to place andamount as to provide a partial over-.- lapping of impregnated layers of,separate solutions from top to bottom over the thickness of the web;"conducting the impregnated web through a precipitation; bath tocoagulate the elastomer after the last solution of the elastomer hasbeen applied. 13. A process as claimed in claim 12 wherein, the initialnon-woven fibrous to be impregnated has a density of about 0.08 to 0.30gram/emf. 4

14. A process as claimed in claim 12 wherein the initial non-wovenfibrous to be impregnated has a density, of about 0.12 to 0.20 gram/emiv 15. A process as claimed in claim .12 wherein the iin-j pregnated webis compressed in the precipitation bath web.

References Cited UNITED STATES PATENTS Fukushima et al 117-63 Dunderdale117-76 T Hochberg 11768 X 10 Hodge et a1 117-76 T 14 Knibbe et a1 117-76TX Saligny et a1 ll763 Russell ll783 Holden 117-135.5

WILLIAM D. MARTIN, Primary Examiner R. HUSACK, Assistant Examiner US.Cl. X.R.

ll765.2, 68, 76 T, 111R, 135.5

